Natural antibodies are dimers and are therefore referred to as bivalent. They have four variable domains, namely two VH domains and two VL domains. The variable domains serve as binding sites for an antigen, a binding site being formed from a VH domain and a VL domain. Natural antibodies recognize one antigen each, so that they are also referred to as monospecific. Furthermore, they also have constant domains which add to the stability of the natural antibodies. On the other hand, they are also co-responsible for undesired immune responses which result when natural antibodies of various animal species are administered mutually.
In order to avoid such immune responses, antibodies are constructed which lack the constant domains. In particular, these are antibodies which only comprise the variable domains. Such antibodies are designated Fv antibody constructs. They are often available in the form of single-chain monomers paired with one another.
However, it showed that Fv antibody constructs only have little stability. Therefore, their usability for therapeutic purposes is strongly limited.
Thus, it is the object of the present invention to provide an antibody by means of which undesired immune responses can be avoided. Furthermore, it shall have a stability which makes it usable for therapeutic uses.
According to the invention this is achieved by the subject matters defined in the claims.